In order to actuate occupant protection devices such as an air bag device or a seat belt pre-tensioner, there is a conventional technology relating to an occupant decision device for a vehicle (hereinafter referred to as an occupant decider) that decides a type of an occupant on a vehicle seat (refer to JP5531471, for example).
In such an occupant decider, it is decided if a vehicle seat is vacant, a state in which a child seat is secured, a state in which a small-build adult is seated, or a state in which a large-build adult is seated, for example, in order to decide an actuation of the occupant protection devices.
Hereinafter, these states of the vehicle seat that are decided by the occupant decider are comprehensively referred to as a type of an occupant.
The occupant decider disclosed in the conventional technology described above has a pair of load sensors disposed on right and left sides of a support portion of the vehicle seat, and decides the type of the occupant on the vehicle seat based of detected values of the load sensors.
Furthermore, the occupant decider calculates a left-right difference load value by subtracting a detected value of one of the load sensors from another detection value of another one of the load sensors.
Then, defining that an absolute value of the left-right difference load value when a buckle of a seat belt device is engaged as a reference value, it is decided that the child seat is attached to the vehicle seat when the absolute value of the left-right difference load value is reduced by a predetermined value from the reference value.
Usually, the detected values of the load sensors increase due to the child seat being tightened strongly by a webbing of the seat belt device when attaching the child seat to the vehicle seat.
In contrast, in the occupant decider according to the conventional technology described above, an erroneous decision that an adult is seated in the vehicle seat can be prevented from occurring in spite of the detection values of the load sensors are increased when the child seat is attached on the vehicle seat.
However, in the occupant decider according to the conventional technology described above, the left-right difference load values on the vehicle seat are calculated, and it is decided that the child seat is attached to the vehicle seat when the absolute value of the left-right difference load value is reduced by the predetermined value from the reference value.
Therefore, there are problems that the calculation for deciding the type of occupant on the vehicle seat becomes complicated, and the time required for calculation is disadvantageously increased.
Further, since errors of the detection values of the pair of the load sensors are accumulated during the calculation, there is a problem that accuracy in deciding the type of the occupant is lowered.